You need to read this book by Jonathan Zdziarski. Even if you’re not
working on a project that handles highly sensitive data, you’ll be amazed how
easy it is to hack into a locked iPhone and extract quite a bit of data if you
have physical access to the device. It’s a great book to learn about the low
level internals. And you’ll be better prepared with techniques to minimize
exposure of private information.

iOS is a juicy target for those hunting effective exploits. This can help you
get into the mindset of someone wanting to attack your users through your
software.